1. Field of the Invention
The present invention relates to a tensioner that provides appropriate tension to a running chain, belt, or the like.
2. Description of the Related Art
It has been common practice to use a tensioner for maintaining appropriate tension in a chain or the like. For example, a known chain guide mechanism, which slidably guides a transmission chain, such as an endless roller chain passing over respective sprockets of a crankshaft and of a cam shaft inside an engine room, uses a tensioner to bias a tensioner lever in order to maintain appropriate tension of the chain or the like.
The known tensioner 510 used in such a chain guide mechanism includes, for example, as shown schematically in FIG. 6, a housing 530 having a cylindrical plunger bore 531 that is open on a front side, a cylindrical plunger 520 slidably inserted in the plunger bore 531, and a biasing unit that biases the plunger 520 toward the front side. The biasing unit is formed by a coil spring 560 accommodated inside a plunger hole 521 of the cylindrical plunger 520 and compressed between the plunger and the housing bottom 532.
Oil is supplied from an oil supply hole 533 formed in the housing 530, so that an oil pressure chamber 512 formed between the plunger bore 531 and the plunger 520 is filled with the oil, which oil biases the plunger 520 toward the front side. A check valve 550 (schematically shown only as a check ball) prevents the oil from flowing out from the oil supply hole 533. As the plunger 520 reciprocates, the oil flows through the small gap between the plunger 520 and the plunger bore 531, and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger 520.
In such a known tensioner 510, when let stand for a long time after the oil supply is stopped (in the case with an engine, after the engine is stopped), there is a time lag before the oil is supplied immediately after the next start-up, and as no oil is replenished but the oil in the oil pressure chamber 512 only leaks out when the plunger 520 moves back and forth, there occurs a shortage of oil in the oil pressure chamber 512. Because of this shortage of oil, the damping force of the oil does not act on the plunger 520, which sometimes may lead to vibration and abnormal noise of the timing chain, or damage on the timing chain.
Therefore, a tensioner is known, such as the tensioner 610 of Japanese Patent Application Laid-open No. 2008-215553 shown in FIG. 7, which is designed to have an oil reservoir chamber 613 inside the plunger 620 to supply oil into the oil pressure chamber 612 from the oil reservoir chamber 613. A constant amount of oil is retained in the oil reservoir chamber 613 such as not to leak out, so that, even immediately after the start-up after a long stop, the oil remaining in the oil reservoir chamber 613 is supplied to the oil pressure chamber 612, to maintain the damping force of oil for the plunger 620, reduce vibration and prevent damage of the chain.
In the tensioner 610 shown in FIG. 7, an inner sleeve 640 is disposed inside the plunger hole 621 on the rear side, so that an internal space formed between the housing 630 and the plunger 620 is divided by the inner sleeve 640 into the oil pressure chamber 612 on the front side and the oil reservoir chamber 613 on the rear side. A check valve 650 is disposed on one side of the inner sleeve 640 facing the oil pressure chamber 612 for preventing the oil from flowing reversely from the oil pressure chamber 612 into the oil reservoir chamber 613, so that a constant amount of oil is retained in the oil reservoir chamber 613 without leakage, and even immediately after the start-up after a long stop, the oil remaining in the oil reservoir chamber 613 is supplied to the oil pressure chamber 612.
In this tensioner 610, a cylindrical ball seat 644 on which a check ball 651 is seated is press-fitted to the front end of the inner sleeve 640 that faces the oil pressure chamber 612. As a result, unlike the case where the ball seat 644 is fixed to the inner sleeve 640 with the use of a biasing force of a coil spring 660, the inner sleeve 640 and the check valve 650 can be assembled together easily.